The invention relates to a backrest for a vehicle seat, having a head restraint which can be adjusted from an in-use position into a safety position under the action of a force-generating device which is effective in an accident situation, said head restraint being connected to the backrest via retaining elements protruding into the backrest.
Even in the case of a relatively minor rear-end impact, vehicle occupants are exposed to the risk of suffering an overextension of the cervical vertebra under the effect of accident-induced acceleration forces. Although head restraints which are connected rigidly to the backrest of the vehicle seat are able to reduce the risk of injury, they are situated, for reasons concerned with comfort, too far away from the head in the in-use position in order to prevent injuries in the neck region effectively. The same is also true if the head restraint has been set to the correct height, corresponding to the vehicle occupant's height, by displacement of its guide rods in the guide sleeves of the backrest.
In order to improve the protection of the occupant, safety devices have therefore been developed which have a head restraint which can be pivoted automatically from the in-use position into a safety position in the event of a rear-end impact, as a result of which its distance from the occupant's head is reduced. Systems of this type are referred to as a “passive head restraint” if the adjustments into the safety position are brought about by the acceleration forces of the occupant acting on the seat. By contrast, if the generator of the adjusting force is fed from a separate power source, the safety system is provided with an “active” head restraint.
The laid-open specification DE 197 38 201 A1 discloses a backrest of the generic type for a vehicle seat. The passive head restraint has guide rods which protrude into the backrest and are guided in a longitudinally displaceable and fixable manner in two spaced-apart sleeves for the purpose of adjusting the height. The lower sleeve is connected directly to the frame structure of the backrest via a rotary joint while the upper sleeve is articulated on the frame structure via a toggle-lever mechanism which is angled in the in-use position. In the event of an accident, the toggle lever is stretched, as a result of which the guide rods rotate about the axis of the lower rotary joint and pivot the head restraint in the direction of the vehicle occupant's head. A leaf spring which is arranged in the lumbar region of the backrest and is curved in the in-use position is used to generate force, the leaf spring being straightened in an accident under the action of the acceleration of the occupant, as a result of which the distance between its ends is increased. This lengthening is transmitted via a mechanism to the toggle lever and changes its position in the previously described manner.
This variant basically has the disadvantage that, depending on the sitting position of the occupant, the leaf spring is insufficiently lengthened. Furthermore, the height of the head restraint, which is frequently set in quite a low position for reasons concerned with comfort, cannot be changed when adopting the safety position.
A backrest having an active head restraint is disclosed in the laid-open specification DE 199 38 904 A1. The backrest is constructed in two parts, the lower part being connected to the seat part of the vehicle seat in a conventional manner, the upper part, in contrast, being pivotable together with the head restraint relative to the lower part about an axis running transversely with respect to the longitudinal axis of the vehicle from an in-use position into a safety position. The torque required for this is generated by a compression spring which acts on a lever, is tensioned in the in-use position of the seat and locked by means of a latching device. The acceleration forces which are produced in a rear-end impact are detected by a vehicle crash sensor. A control device releases the latching device by triggering a pyrotechnic activator as soon as acceleration values which exceed a predetermined threshold value are measured.
This device satisfies the requirements placed on it in respect of the safety of the vehicle occupants, but is associated with being relatively complex in terms of design.